OMC 4.3L Cobra 1988 *Appeared* to Seize

[frank1492]

Engine quickly died at acceleration to about 3K RPM. Heard "clunk" and backfire. Starter strains to turn engine, can only turn slowly and intermittently. Oil level fine, engine cold. Ran extremely smoothly before quitting. No evidence of mechanical rattles or pending oil pump failure.
After a few minutes engine seems to turn over fine at high speed, but no start. (Had previous tendency to hard start after running.) Starter eventually seemed to bind again, but this time I suspect the starter as it was in the process of burning out after having been strained for several minutes.
(Burning smell, then quit.)
At shop, starter diagnosed as burned out. Initial check showed perfect plugs, engine could be turned manually with normal resistance. Prop spun fine, no evidence of metal fragments in drive oil, all oil levels normal.
While I await the arrival of a new starter, does anyone have any ideas? I should note that the engine drop in RPMs, while sudden, sounded as if it could also have been caused by an electrical failure. Earlier there had been a short period of rapid, rhythmic "bucking," as if intermittent ignition failure. I had just replaced the spark plug wires.
When the new starter arrives, the shop plans to try to get the engine started. If the starter shows resistance, they will detach the stern drive and try again.
What would you do, and what could this be? I am a little afraid it will turn out to be something intermittent that will drain my wallet. (I know- it's a boat. Actually I am used to having my wallet drained.)
Help much appreciated!
Frank

 

[a70eliminator]

Re: OMC 4.3L Cobra 1988 *Appeared* to Seize

From your description I'm going to say your timing chain jumped a tooth, verify your still firing on #1 by looking at the rotor with timing marks at TDC, between the backfire and laboring starter it's my best guess.

 

[HT32BSX115]

Re: OMC 4.3L Cobra 1988 *Appeared* to Seize

Hi Frank,



You might provide some additional info.

Was 3000 RPM all it would turn at WOT?

When you say HARD START......did it crank "ok" but not start or did it crank like the battery was "dead"?



Was there ANY water in any cyl when you turned the engine with the plugs out?

Did you or anyone else change the drive lubricant recently?

If you replaced the plug wires, did you possibly "crimp" one such that it might have a small cut and be shorting out someplace AND is it possible that you have a couple of wires on the wrong plugs?

If the sudden stoppage is ignition, the engine should have turned over with no problems. It's unlikely that the starter failed at the same time as the ignition.


Regards,


Rick

 

[MikDee]

Re: OMC 4.3L Cobra 1988 *Appeared* to Seize

Okay, take off your distributor cap, and then crank it over,,, to see if the rotors broken, or if it turns or not, while cranking, that might give you an idea if the distributor, camshaft, or timing chain, has broken

 

[Bt Doctur]

Re: OMC 4.3L Cobra 1988 *Appeared* to Seize

Anybody bother to check the oil in the outdrive yet?

 

[frank1492]

Re: OMC 4.3L Cobra 1988 *Appeared* to Seize

Please note that after the initial laboring, the starter appeared to turn freely indicating the engine was no longer binding. And if the timing chain skipped a tooth I'd expect sudden deterioration in performance not a dead stall. I had an engine once with a plastic timing gear that did this. (Thank you for your idea!)

 

[frank1492]

Re: OMC 4.3L Cobra 1988 *Appeared* to Seize

Died at about 3000 on acceleration.
Oil was clean- no water.
Lube changed about a year ago.
Brand new Die-Hard Marine battery, starter about one year old, had previously run flawlessly. Would be huge coincidence if, say, ignition failure, then simultaneous starter malfunction, wouldn't you think? (Thank you for your idea!)

 

[frank1492]

Re: OMC 4.3L Cobra 1988 *Appeared* to Seize

To clarify, starter initially turned engine slowly, eratically, with burning smell after awhile, then later appeared to turn engine at normal speed before quitting. If starter simply had a bad or erratic connection, I don't think it would have burned out. It would seem it had to be laboring at some point.

 

[frank1492]

Re: OMC 4.3L Cobra 1988 *Appeared* to Seize

I will advise them to look at the distributor- I sense electrical is involved in some way. (Thank you!)

 

[frank1492]

Re: OMC 4.3L Cobra 1988 *Appeared* to Seize

The oil in the outdrive was checked. (Thanks!)

 

[MikDee]

Re: OMC 4.3L Cobra 1988 *Appeared* to Seize

I had 2 different vehicles, with separate occasions that happened like this, 1) Was a distributor disintegrated inside, and 2) A camshaft snapped after the first lobe, both vehicles were not neglected, and driving normally at the time

 

[frank1492]

Re: OMC 4.3L Cobra 1988 *Appeared* to Seize

I had 2 different vehicles, with separate occasions that happened like this, 1) Was a distributor disintegrated inside, and 2) A camshaft snapped after the first lobe, both vehicles were not neglected, and driving normally at the time

May I ask if your symptoms were *exactly* the same as mine, or just approximate, and if approximate in what ways did they differ? And how easy were these to fix? Thanks.

 

[frank1492]

Re: OMC 4.3L Cobra 1988 *Appeared* to Seize

May I ask if your symptoms were *exactly* the same as mine, or just approximate, and if approximate in what ways did they differ? And how easy were these to fix? Thanks.

And most important, did the starter labor in both these cases?

 

[MikDee]

Re: OMC 4.3L Cobra 1988 *Appeared* to Seize

May I ask if your symptoms were *exactly* the same as mine, or just approximate, and if approximate in what ways did they differ? And how easy were these to fix? Thanks.

When the cam snapped on my 62' Chevy Impala SS 327, I just heard a clunk, and the engine died.

Many yrs later, when my distributor broke inside, it was almost the same noise, & the engine died.

You can't compare these generic symptoms, to what you have, sometimes it's impossible to diagnose an engine problem by the noise it makes, a snap. crackle, & pop, or clunk, could be anything? You need to start checking the external, or internals of your engine. I gave you a good starting point to begin with, did you check it out?

 

[frank1492]

Re: OMC 4.3L Cobra 1988 *Appeared* to Seize

When the cam snapped on my 62' Chevy Impala SS 327, I just heard a clunk, and the engine died.

Many yrs later, when my distributor broke inside, it was almost the same noise, & the engine died.

You can't compare these generic symptoms, to what you have, sometimes it's impossible to diagnose an engine problem by the noise it makes, a snap. crackle, & pop, or clunk, could be anything? You need to start checking the external, or internals of your engine. I gave you a good starting point to begin with, did you check it out?

Will head for the boatyard later today and report back. Thanks.

 

[frank1492]

Re: OMC 4.3L Cobra 1988 *Appeared* to Seize

It was water in the engine. The starter was trying to push the water out, that's why it labored. Now very low compression on starboard side, mixed values on port.
The work stopped at that point, but I suspect the cause was a leaking water jacket. The combo manifold/risers were 11 years old.
Had planned to replace the manifolds....soon...
Thanks all for your help!
Frank

 

[Gary H NC]

Re: OMC 4.3L Cobra 1988 *Appeared* to Seize

Time to pull the heads and hope for the best..
And order some manifolds if the engine is not gone..
At least the replacement kits have dropped in price a little and they are a 2 piece manifold and riser..

 

[HT32BSX115]

Re: OMC 4.3L Cobra 1988 *Appeared* to Seize

It was water in the engine. The starter was trying to push the water out,

We call that a "hydrolock" (since you cannot "push" water past a closed intake and exhaust valves) One of the reasons that one should remove the risers once in a while and inspect/replace the riser-gaskets.

Right when you shut an engine down there's water in the risers above those gaskets all the way up to the top of the risers.

While the engine is running, the exhaust keeps any water from gasket leaks from making it to the exhaust valves and into the engine.

When the engine stops the water level in the riser/manifolds drops quickly but not before some might leak past the riser gasket(s) and into the exhaust manifold and into open exhaust valves.

That water will sit on top of the piston until it evaporates, leaks past the rings or you try to start it later......

If it sits for the winter, well, you can imagine what it does to the inside of the cyl.

If you try to start it before the water evaporates or leaks past the rings, you get a little hydrolock action.

This is what happened every time I tried to start my former High Technology OMC 460.... a cyl on both sides was severely rusted from sitting for a winter. It hydrolocked every time I tried to start it after running. If it sat for more than a few hours or over night it would start normally but would barely crank and seemed like a dead battery when attempting a start within 10 min or so of shut down.....like picking up a skier.

I was going to replace the manifolds and risers when I found out they couldn't be bought at any price.......

So I fixed it a different way.....


Cheers,

Rick

 

[frank1492]

Re: OMC 4.3L Cobra 1988 *Appeared* to Seize

Time to pull the heads and hope for the best..
And order some manifolds if the engine is not gone..
At least the replacement kits have dropped in price a little and they are a 2 piece manifold and riser..

I opted to go with a Merc rebuilt long block. I just couldn't see doing a rebuild on a 21 year old engine with salt water running through it. The block was $2850 plus 16 hours labor. I'd guess a rebuild might have saved me $1000-1500 or so, if it could be done. What do you say?

 

[frank1492]

Re: OMC 4.3L Cobra 1988 *Appeared* to Seize

I was going to replace the manifolds and risers when I found out they couldn't be bought at any price.......

Thanks Rick for your great explanation. See my earlier post as to what I plan to do.
As for the riser/manifolds, for the V6 4.3L, the Osco two-piece kit runs over $1200 if you buy it from Osco. I found a cache of the original one-piece riser manifold combo (OMC original) at $800 each. For the difference in price I decided to go for these. Fewer gaskets seems like a good idea, but I suppose the two piece approach allows for easier inspection. What do you think?
And every how often would you replace these? Mine might have been on for the full age of the boat (21 years) as I bought it ten years ago used. The manifolds looked pretty new then, but who knows?